Refs #2146 (items: `/api/nodes/:pubkey/battery`, `/api/perf`).
## Situation
Two endpoints ran SQL that reads more than it needs, on every request.
Timings are read-only on a production database (18.3M observations, 283k
`observer_metrics` rows), first run / second run:
| Query | Now | With this PR |
|---|---|---|
| battery history, `WHERE LOWER(observer_id) = ?` | 174 / 29 ms (plan:
`idx_observer_metrics_timestamp`) | 5.9 / 5.5 ms (plan: primary key
`(observer_id, timestamp)`) |
| `/api/perf`: `SELECT COUNT(*) FROM observations` | 118 / 116 ms on
every call | once per 60 s |
## My changes in this PR
1. **Battery history** (`5bdd3c7f`). `LOWER(observer_id) = ?` keeps
SQLite off the primary-key index, so it walked the timestamp index over
every observer's metrics in the window. The query now matches
`observer_id IN (?, ?)` with the pubkey lowercased and uppercased, the
two casings observer IDs are stored in.
2. **`/api/perf` row counts** (`e24c24cf`). The four `COUNT(*)`
(transmissions, observations, nodes, observers) are cached for 60 s.
File, WAL and freelist sizes are still read on every call.
## Tests
- `TestNodeBatteryQueryUsesObserverIndex` loads the `sqlite_stat1`
values of that database and checks the plan uses
`sqlite_autoindex_observer_metrics_1`. With the `LOWER()` form it fails
with `SEARCH observer_metrics USING INDEX idx_observer_metrics_timestamp
(timestamp>?)`.
- `TestGetNodeBatteryHistory_LowercaseStoredID`: a lowercase-stored
observer ID is still found.
- `TestGetDBSizeStatsTypedCachesRowCounts`: the cached count is served
within the TTL and refreshed after it.
- `cmd/server`: `go test ./...` green.
## Not in this PR
Other per-request queries listed in #2146 measured too small to change
on the same database: `COUNT(*) FROM dropped_packets` 0.0 ms, `SELECT
DISTINCT iata FROM observers` 0.2 ms, the observers packet-count query
1.3 ms, the 7-day active node count 0.1 ms. An observer ID stored in
mixed case would no longer match the battery query; in that database all
41 distinct `observer_metrics.observer_id` values are uppercase.
---------
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
## Summary
Closes#663 (Phase 2 + 3 partial — time-series tracking + thresholds for
nodes that are also observers).
Adds a per-node battery voltage trend chart and
`/api/nodes/{pubkey}/battery` endpoint, sourced from the existing
`observer_metrics.battery_mv` samples populated by observer status
messages. No new ingest or schema changes — purely surfaces data we were
already collecting.
## Scope (TDD red→green)
**RED commit:** test(node-battery) — DB query, endpoint shape
(200/404/no-data), and config getters all asserted.
**GREEN commit:** feat(node-battery) — implementation only.
## Changes
### Backend
- `cmd/server/node_battery.go` (new):
- `DB.GetNodeBatteryHistory(pubkey, since)` — pulls `(timestamp,
battery_mv)` rows from `observer_metrics WHERE LOWER(observer_id) =
LOWER(public_key) AND battery_mv IS NOT NULL`. Case-insensitive join
tolerates historical pubkey casing variation (observers persist
uppercase, nodes lowercase in this DB).
- `Server.handleNodeBattery` — `GET /api/nodes/{pubkey}/battery?days=N`
(default 7, max 365). Returns `{public_key, days, samples[], latest_mv,
latest_ts, status, thresholds}`.
- `Config.LowBatteryMv()` / `CriticalBatteryMv()` — defaults 3300 / 3000
mV.
- `cmd/server/config.go` — `BatteryThresholds *BatteryThresholdsConfig`
field.
- `cmd/server/routes.go` — route registration alongside existing
`/health`, `/analytics`.
### Frontend
- `public/node-analytics.js` — new "Battery Voltage" chart card with
status badge (🔋 OK / ⚠️ Low / 🪫 Critical / No data). Renders dashed
threshold lines at `lowMv` and `criticalMv`. Empty-state message when no
samples in window.
### Config
- `config.example.json` — `batteryThresholds: { lowMv: 3300, criticalMv:
3000 }` with `_comment` per Config Documentation Rule.
## Status semantics
| latest_mv | status |
|-----------------------|------------|
| no samples in window | `unknown` |
| `>= lowMv` | `ok` |
| `< lowMv`, `>= critMv`| `low` |
| `< criticalMv` | `critical` |
## What this PR does NOT do (deferred)
The issue's full Phase 1 (writing decoded sensor advert telemetry into
`nodes.battery_mv` / `temperature_c` from server-side decoder) and Phase
4 (firmware/active polling for repeaters without observers) are out of
scope here. This PR delivers the requested Phase 2/3 surfacing for the
data path that already lands rows: `observer_metrics`. Repeaters that
are also observers (i.e. publish status to MQTT) will get a voltage
trend immediately; pure passive nodes won't until Phase 1 lands.
## Tests
- `TestGetNodeBatteryHistory_FromObserverMetrics` — case-insensitive
join, NULL skipping, ordering.
- `TestNodeBatteryEndpoint` — full happy path with thresholds + status.
- `TestNodeBatteryEndpoint_NoData` — 200 + status=unknown.
- `TestNodeBatteryEndpoint_404` — unknown node.
- `TestBatteryThresholds_ConfigOverride` — config getters + defaults.
`cd cmd/server && go test ./...` — green.
## Performance
Endpoint is per-pubkey (called once on analytics page open), indexed by
`(observer_id, timestamp)` PK on `observer_metrics`. No hot-path impact.
---------
Co-authored-by: bot <bot@corescope>
